A file server is widely used for a simple method to share a file. The file server has been used for a relatively small group of users of client terminals as a file server in a department (a department file server). That is, the server has been used by a relatively small group of end users. In these years, integration of the file servers is promoted for the purpose of improvement of performance of equipments such as an NAS (Network Attached storage; an exclusive appliance for file server) and a server, and information integration trend. The integrated file servers have a size of a few terabytes and are used in the scale of thousands of users.
Such file servers are different from a conventional department file server, and are required to certainly backup data and operate around-the-clock without any down time. That is, it can be said that the integrated file servers are made to be used in a large scale and built as an infrastructure.
A maintenance cost increases in accordance with the usage in a large scale as an infrastructure of the file servers. Accordingly, reduction of the maintenance cost is a major problem for a user (an administrator) of the file server.
The administrator has to manage all files at a level for a most important file. However, all of the files stored in the file server are not necessarily important. Accordingly, the ordinarily-unnecessary maintenance cost for “regular backup”, “storage for redundancy”, “storage of access logs”, and the like is also generated to the files unrelated to business. Such generation of the unnecessary maintenance cost occurs through even management of all the files without relation to a file attribution.
In order to handle such problems, various techniques for changing a management method in accordance with the file attributions such as importance of the files are developed and proposed. For example, a Hierarchical Storage Management (HSM) for moving a file of low importance to a low cost storage is proposed. When these methods are employed, the maintenance cost can be reduced, but indeed there is a problem that it is difficult to classify the files. In the conventional department file server, the administrator could classify the files because the number of end users is small. However, when the file servers are used in a large scale as an infrastructure, the administrator deals with up to thousands of end users and thus cannot know the importance of each file.
For example, the Hierarchical Storage Management (HSM) employs attributions such as an update time, an access time, and an access history of a file as a policy to classify the file. This is based on a concept that “a file that is accessed is highly important and requires a high performance” and “a file that is not accessed is less important and does not require a high performance”. This policy is rational in a total performance. However, it is actually difficult to evenly classify all the files stored in the file server by using only the policy. As a matter of fact, among all the files, there are so many files that are not frequently accessed in the file server by a client terminal but are important. If the HSM moves such files to a low-speed storage, a problem of delaying an access time to the file may occur.
In the department file server that is accessed by a small group of end users, the administrator can know which file is important, but in the file servers accessed in the scale of hundreds of or thousands of end users, the administrator cannot know that and determine the policy simply.
In addition, when the file servers are used in a large scale as an infrastructure, the administrator generally tends to strongly believe that he works as an infrastructure administrator and not to concern contents of the files. On the contrary, a method can be considered in which the administrator does not set an importance level of whether or not each file is important, to each file but an end user dealing with the file sets the importance levels to all files by opening an administration GUI (Graphical User Interface) and commands to the end user. However, it will cause a matter of system security that anyone of thousands of end users can change the setting of the importance level.
It should be noted that “Proposal of the Command File Method for Management Operation of Extended File system Function by Users” (FIT2006: 5th Forum on Information Technology) is made by Ishida and Sonoda, to propose a method for realizing a file system extension function by using a command file allocated on a directory. In this method, the command file is produced by a client program in a client terminal.
In order to efficiently manage the files with reduction of the maintenance cost, it is required to set an importance level to each of files and to appropriately reduce the maintenance cost. However, when the administrator sets the importance level to each file, the administrator has to check contents of all files to determine the levels, and accordingly the case cannot be realized substantially in the file servers used in a large scale as an infrastructure.